1. Field of the Invention
The present invention relates to a liquid discharge recording apparatus (an ink jet recording apparatus) and a liquid discharge recording method (an ink jet recording method) for recording by a liquid discharge recording system (an ink jet recording system) including discharging a liquid from a discharge port to form pixels on a print material and forming an image from the pixels.
2. Related Background Art
With the widespread use of information processing equipment such as a copier, a work processor or a computer, and communications equipment, an apparatus for recording digital images using a liquid discharge head (an ink jet head) has been rapidly widely used as an image forming apparatus or a recording apparatus for such equipment. There has been an increasing need for a recording apparatus adapted for high quality images and color images as information processing equipment and communications equipment have processed high quality or color visual information.
Such a recording apparatus has used a liquid discharge head having nozzles each including a discharge port of ink (a liquid) and a channel placed at high density in order to obtain finer pixels in response to the need for high quality images. Also, the recording apparatus generally includes ink heads for discharging ink of, for example, cyan, magenta, yellow and black for coloring. Further, the recording apparatus is required to perform a recording operation at higher speed while allowing formation of high quality images, and thus the liquid discharge head has included a larger number of nozzles in order to increase the number of pixels formed at a time to increase the recording speed.
In particular, a method has been embodied such that a liquid discharge head is formed to have a length substantially equal to a width of a maximum print material for recording to allow recording in one pass scan, thereby allowing high speed output. In this case, for a page printer set for A4 paper in a landscape orientation, a length of a liquid discharge head is about 30 cm, and approximately 14000 or more nozzles are required at a nozzle density of 1200 dpi (dot per inch). Manufacturing such a liquid discharge head having a large number of nozzles at a time requires a large machine body, which causes problems in terms of manufacturing costs and yields.
Further, the large number of nozzles prevents all the nozzles from having and maintaining the same performance. This may cause uneven ink discharge amounts or shifted (skewed) dot placement positions between the nozzles, and using a technique of head shading correction has been known for preventing uneven optical densities of recorded images.
General head shading is a method of measuring an optical density of an output pixel for each nozzle to feedback the results to input image data for correcting uneven optical densities. For example, when a certain nozzle discharges a smaller amount of ink for some reasons, and an optical density of that portion is low, correction for increasing a tone level of an input image at a portion corresponding to the nozzle, thereby providing even optical densities of an output image.
The large number of nozzles may include non-discharge nozzles, and a technique of non-discharge nozzle correction (non-discharge supplement) has been known for performing supplementary processing to allow image output even if all the nozzles are not perfect.
Known methods of non-discharge supplement includes a method in which with a non-discharge nozzle, nozzles on both sides of the non-discharge nozzle are used to form dots (pixels) on positions adjacent to a dot (pixel) to be formed by the non-discharge nozzle, or a method of correcting image data for a recording operation so as to include dots around a dot to be formed by a non-discharge nozzle (adjacent supplement). A method of forming an ink dot of a different color such as black on a portion on which a dot is to be formed by a non-discharge nozzle of cyan for supplement (different color supplement) is also known.